The present invention relates to an electrical conductor winding and to a method of manufacturing an electrical conductor winding. The present invention relates in particular to an electrical conductor winding for an active electromagnetic bearing, an electrical generator or an electrical motor for use at relatively high temperatures.
At the present electrical machines comprise one or more electrical conductor windings each of which has a polymeric insulation material. These electrical machines have a maximum operating temperature of the order of 200xc2x0 C., due to the polymeric insulation material applied to the electrical conductor windings.
The use of specialist high temperature polymeric insulation material would enable the electrical machines to have a maximum operating temperatures of the order of 250xc2x0 C. However, it is believed that stable, oxidation resistant, polymeric insulation material will not have maximum operating temperatures above 300xc2x0 C.
There is a requirement for electrical machines with maximum operating temperatures of the order of 500xc2x0 C. and above. These electrical machines for example are active electromagnetic bearings, electrical generators and electrical motors for use within gas turbine engines, particularly on the high-pressure shaft/rotor of a gas turbine engine. The use of active electromagnetic bearings may allow the simplification of the gas turbine engine by elimination of conventional bearings and oil systems.
As discussed above polymeric insulation material cannot be used at temperatures above about 300xc2x0 C.
The use of an inorganic insulation material for the electrical conductors is a possibility. The inorganic insulation material may be based on ceramic cloths or ceramic coatings, applied to the electrical conductors. However, this is not desirable because the inorganic insulation material tends to be bulky limiting the packing density of the electrical conductor and the electrical conductors require potting in an inorganic cement. Additionally the manufacturing process is very labour intensive.
The use of an inorganic insulation material may be based on ceramic cloth and inorganic cement. However, this is not desirable because these inorganic insulation materials have poor thermal conductivity and would make the thermal management of the electrical conductor difficult. Additionally the porous nature of the inorganic cement tends to allow the inorganic insulation material to soak up fluids, for example water, oil or other lubricant. The presence of moisture tends to degrade the electrical insulation by allowing leakage currents to earth or between turns of the electrical conductor. The presence of oil tends to degrade the electrical insulation by forming carbon also allowing leakage currents to earth or between turns of the electrical conductor. Also the thermal expansion mismatch may cause damage to the insulation material during thermal cycling of the electrical conductor.
The present invention seeks to provide a novel electrical conductor winding which reduces, preferably overcomes, the above mentioned problems. The present invention also seeks to provide a novel method of manufacturing an electrical conductor winding.
Accordingly the present invention provides an electrical conductor winding comprising a plurality of laminates of electrical insulation, each laminate of electrical insulation having a first surface and a second surface, the first surface of each laminate of electrical insulation being flat and the second surface of each electrical insulation having a slot, at least one aperture extending through each laminate of electrical insulation from the slot to the first surface, each laminate of electrical insulation having an electrical conductor arranged in the slot, each aperture having an electrical connector to connect the electrical conductor in the slot in one laminate of electrical insulation with the electrical conductor in the slot in an adjacent laminate of electrical insulation, the laminates of electrical insulation being arranged such that the first surface of one laminate of electrical insulation abuts and is bonded to the second surface of an adjacent laminate of electrical insulation and the laminates of electrical insulation comprises a glass-ceramic material, the glass-ceramic material comprises at least one phase whose combined thermal expansion substantially matches the thermal expansion of the electrical conductor.
Preferably the at least one phase includes cristobalite, lithium zinc silicate, lithium disilicate, lithium metasilicate, enstatite, clinoenstatite or calcium orthosilicate.
Preferably the glass-ceramic material comprises silica, lithium oxide, zinc oxide, potassium oxide and phosphorus oxide.
One suitable glass-ceramic material comprises 59.2 wt % SiO2, 9.0 wt % LiO2, 27.1 wt % ZnO, 2.0 wt % K2O and 2.7 wt % P2O5.
The glass material comprising 12 to 14.5 wt % Li2O, 2 to 2.6 wt % ZnO, 4.7 to 5.7 wt % K2O, 8.2 to 10.2 wt % Al2O3, 0.31 to 0.39 wt % starch, 0.027 to 0.033 wt % CeO2, 0.018 to 0.022 wt % AgCl and the balance SiO2 plus incidental impurities.
Preferably the electrical conductors comprise copper.
Preferably the electrical connectors comprise copper.
Preferably the electrical connectors are brazed to the electrical conductors.
Alternatively the electrical connectors are soldered to the electrical conductors by high electrical conductivity solder.
Preferably at least one of the electrical conductors is wound into a spiral. Preferably each of the electrical conductors is wound into a spiral.
Preferably the electrical conductor winding comprises an active electromagnetic bearing, an electrical generator or an electrical motor.
The present invention also provides a method of manufacturing an electrical conductor winding comprising
(a) forming a plurality of laminates of electrical insulation, each laminate of electrical insulation having a first surface and a second surface, the first surface of each laminate of electrical insulation being flat, the second surface of each laminate of electrical insulation having a slot, the laminates of electrical insulation comprises a glass or a glass-ceramic material, the glass-ceramic material comprises at least one phase whose combined thermal expansion substantially matches the thermal expansion of the electrical conductor,
(b) forming at least one aperture through each laminate of electrical insulation from the slot to the first surface,
(c) placing an electrical conductor in the slot in each laminate of electrical insulation,
(d) placing an electrical connector in the aperture in each laminate of electrical insulation to connect the electrical conductor in the slot in one laminate of electrical insulation with the electrical conductor in the slot in an adjacent laminate of electrical insulation,
(e) stacking the laminates of electrical insulation such that the first surface of one laminate of electrical insulation abuts the second surface of an adjacent laminate of electrical insulation,
(f) heating the stack of laminates of electrical insulation such the first surface of one laminate of electrical insulation bonds to the second surface of an adjacent laminate of electrical insulation.
The method may comprise an additional step (g) after or concurrent with step (f) of heating the stack of laminates of electrical insulation to convert the glass to a glass ceramic material.
Preferably the method comprises placing a layer of glass powder between the laminates of electrical insulation to bond the laminates of electrical insulation.
Preferably the method comprises electroforming the electrical conductors into the slots in the laminates of electrical insulation.
Preferably the electrical conductors comprise copper.
Preferably the method comprises forming the apertures in the laminates of electrical insulation at the same time as forming the slots in the electrical insulation.
Preferably the method comprises forming the apertures through the electrical conductors while the electrical conductor are in the slots.
Alternatively the method comprises forming the apertures through the electrical conductors while the electrical conductors are placed in the slots.
Preferably the electrical connectors comprise copper.
Preferably the method comprises placing a solder material or braze material between the electrical conductors and the electrical connectors.
The method may comprise press forming the laminates of electrical insulation in the glassy state and then turning the laminates of electrical insulation to a glass-ceramic.
Preferably the at least one phase includes cristobalite, lithium zinc silicate, lithium disilicate, lithium metasilicate, enstatite, clinoenstatite or calcium orthosilicate.
Preferably the glass-ceramic material comprises silica, lithium oxide, zinc oxide, potassium oxide and phosphorus oxide.
A suitable glass-ceramic material comprises 59.2 wt % SiO2, 9.0 wt % LiO2, 27.1 wt % ZnO, 2.0 wt % K2O and 2.7 wt % P2O5.
The method may comprise forming the slots in the laminates of the electrical insulation by photo-forming a glass material.
The method may comprise directing ultra violet light onto predetermined regions of the glass material, heat treating the glass to introduce crystal nucleation and growth in the predetermined regions of the glass material exposed to the ultra violet light, etching the glass material to remove glass material in the predetermined regions of the glass material to form the slots.
The glass material comprising 12 to 14.5 wt % Li2O, 2 to 2.6 wt % ZnO, 4.7 to 5.7 wt % K2O, 8.2 to 10.2 wt % Al2O3, 0.31 to 0.39 wt % starch, 0.027 to 0.033 wt % CeO2, 0.018 to 0.022 wt % AgCl and the balance S1O2 plus incidental impurities.